The present invention generally relates to rock drilling bits of the rolling cutter variety and more specifically is directed to an internal lubrication system for a rolling cutter bit.
Conventional rolling cutter drill bits in use today generally utilize a lubrication system which could be classified as a static system. Basically, the system comprises a lubrication supply channel connected to a lubrication reservoir. Usually the lubrication reservoir has a spring-loaded plunger or other resilient biasing means to maintain a continual pressure on the lubricant in hopes that it will force a regular supply of the lubricant into the bearing area. Other types of lubricant supply systems which have been tried in prior devices include downhole electric motor-driven pumps, hydraulic pumps driven by the well fluids being pumped down the borehole during the drilling operations and gear-driven pumps driven by the rotation of the drill string during the drilling operation. Generally these types of pumping systems are complex, heavy, and take up considerable additional space in the drilling equipment, which space is sometimes a critical limitation and may not be available for such devices. The widespread system comprising the spring-loaded reservoir usually does not provide a positive circulation of lubricant through the critical bearing area in the rock bit and thus does not give the needed lubricant protection. The present invention overcomes the deficiencies of the conventional methods by providing a highly efficient, extremely powerful internal lubricant pump requiring no additional room in the drill bit design yet allowing extremely strict control over the pumping action and providing a positive lubricant displacement system in the critical bearing area. The present invention provides a pumping system utilizing the shear forces on the lubricant which are generated by placing a grooved rigid surface in contact with a sliding elastomeric surface to provide positive displacement of the lubricant through the bit structure.